Method and apparatus for constructing make-alive electrodes



Dec. 1, 1942. I Y A. H. TOEPFER- 2,303,515

METHOD AND APPARATUS FOR CONSTRUCTING MAKE-ALIVE ELECTRODES Filed May'7, 1942 I fl g Z.

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" WITNESSES: Q I INVENTOR X2 flaa/p/z fi Taepfen ATTORNEY LWJMW PatentedDec. 1, 1942 METHOD AND APPARATUS Eon coN- STRUCTING MAKE-ALIVEELECTRODES Adolph H. Toepfer, Wilkinsburg, Pa., assignor to WestinghouseElectric & Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application May 7, 1942, Serial No. 442,068

7 Claims. (01. 250-275) The materials heretofore found most suitable foruse as make-alive electrodes are generally hard abrasive materials suchas boron carbide or silicon carbide and the construction of suitablemake-alive shapes has been extremely difficult. The best methodheretofore discovered for producing these shapes has been to shape acarbon or graphite rod to the desired shape of the final electrode andthen convert the graphite material in an electric furnace to asubstantial boron carbide composition. However, a great many blanks arespoiled in the manufacturing operation and other unforeseeabledifficulties produce undesirable electrodes so that it is necessary todiscard a great many apparently finished electrodes to secure thedesired uniformity of the electrodes actually put in service.

It has heretofore been proposed) to construct the electrodes ofrelatively finely divided makealive material held together by suitablebinders but the extremely fragile nature of the originally moldedelectrodes has militated against such construction.

Since it is desirable to heat-treat the make alive electrodes at arelatively high temperature, I have discovered that the electrodes canbe formed in relatively thin metal molds shaped either by drawing sheetmetal blanks or by winding up a strip material such as wire on asuitable form, mold the material within the form, attach a suitableconducting head preferably of graphite, and heat-treat the materialwithin the form itself, finally raising the temperature above themelting point of the metal, such as iron or steel usually utilized forthe form, and removing the form by melting it away. This method producesextremely uniform electrodes, both as to physical dimensions andelectrical characteristics.

It is therefore an object of my invention to provide a simple method offorming make-alive electrodes.

It is a further object of my invention to provide an electrode havinguniform physical dimensions and electrical characteristics.

It is a further object of my invention to provide an electrode moldwhich can be removed when melting the same from the sintered electrode.

Other objects and advantages of my invention will be apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawing, in which:

Figure 1 is a sectional elevation of a sheet metal mold according to myinvention;

Fig. 2 is a sectional elevation through a heat treating furnace showingthe application of my invention to the construction of an electrode; 7

Fig. 3 is a plan view showing the method of constructing a mold fromstrip material;

Fig. 4 is a cross-sectional elevation showing the utilization of thewound mold form;

Fig. 5 is a similar view of a modification of the strip mold accordingto my invention, and

Fig. 6 is an elevational View of a make-alive electrode constructedaccording to my invention.

In the embodiment of my invention according to Figs. 1 and 2 of thedrawing, a piece of sheet metal is drawn or otherwise shaped to providea mold I having an interior of the shape desired for the finishedelectrode. The mold l is then filled with a composition 2 of make-alivematerial such as powdered boron carbide or silicon carbide held togetherwith a suitable binder, preferably an organic material of thehydrocarbon group. I have found that materials such as sugar andstarches are particularly suitable as a binder material.

In order to attach a head 3 or conducting connector to the make-alivebody 2, a head 3 is constructed of suitable conducting material such asgraphite, and pressed into firm contact with the material 2 filling themold. The mold I and its assembled material is then placed in a suitablefurnace 4 preferably of the electric arc type in a non-oxidizingatmosphere and sintered at a temperature of the order of 1200 C., orover, which carbonizes the binding material and firmly bonds it to theconducting connector 3 while this temperature removes the mold metal byreducing it to a fluid which drains away, leaving the finished electrodeunchanged from the shape of the original mold cavity. The resultingelectrodes have been found to have very desirable physicalcharacteristics in that they are tough, and hard, and have the desiredshape without further grinding or mechanical treatment. Also, because ofthe uniformity of shape and construction the electrical characteristicshave been found much more uniform than in hereofore constructed de--vices.

Instead of constructing the mold I from a sheet material, a mold 5 maybe constructed from strip material such as wire by winding the same on amandrel l. The wire mold 5 is filled with the make-alive material 2 inexactly the same manner as the drawn mold l is filled and treated in thesame manner to properly sinter and bond the make-alive electrode andmelt away the wire mold 5.

I have also found that when utilizing a, wire mold the material 2 can besintered for several for the mold material 6, as'these metals tend tocontaminate the make-alive electrode when the sintering temperature israised above the melting point of the metal. However, when.non-contaminating materials such as ironorsteel are utilized for themold material 6, I prefer to melt the wire from the electrode ratherthan remove it in a prefinished state.

A further advantage of the wound mold 5 lies in the fact that theindividual coils ID of the form 5 may be separated a suitable distancell and the make-alive mixture 2 is pressed, not only into the interiorof the form 5, but into the interstices ll between the windings l0, sothat when the electrode 12 is finished, it will present an exteriorsurface having a spiral groove l3 for reducing the operating current asdisclosed in Slepian Patent No. 2,246,326.

It will thus be. seen that I have provided a cheap and readily utilizedform for providing molded electrodes of any desired shape or physicaldimension and also a form that can be readily removed without destroyingthe molded material.

While, for purposes of illustration, I have shown and described specificembodiments of my invention, it will be apparent that changes andmodifications can be made therein without departing from the true spiritof my invention or the scope of the appended claims.

I claim as my invention:

1. The method of constructing a make-alive electrode which compriseswinding a strip metallic material to provide a mold having a mold cavityconforming to the desired shape of the finished electrode, filling themold cavity with particles of high resistant material and an organicbinder material, securing a graphite head to said filling and heattreating the assembly at a temperature above the melting point of themold.

4 2. The method of constructing a make-alive electrode whichcomprises'winding a strip metallic material to provide a mold having a mold cavityconforming to the desired shape of the finished electrode, filling themold cavity with particles of high resistant material and an organicbinder material, securing a graphite head to said filling, sintering thecombination at a temperature below the melting point of the metallicmaterial and then heat treating at a temperature above the melting pointof the metallic material.

I mixture and heating treating said electrode at a temperature of theorder of 1200 C. for a period of the order of three hours.

5. The method of constructing a boron carbide electrode which comprisesconstructing a substantially conical metal mold, filling said mold witha paste composed of boron carbide and a hydrocarbon binder, assembling aconducting head in contact with said paste and melting the metal moldfrom the assembly in a non-oxidizing atmosphere.

6. The method of constructing a make-alive electrode which compriseswinding a metallic strip into a mold, filling said mold with a mixtureof high resistant material and an organic binder,

-pressing a conducting head into contact with

